Assay for human erythrocyte pyridoxine kinase

Effects of the color additive caramel color III and 2-acetyl-4(5)-tetrahydroxybutylimidazole (THI) on the immune system of rats

Administration of ammonia caramel color (AC) to rats may decrease blood lymphocyte counts, specifically in rats fed a diet low in vitamin B6. This effect is associated with 2-acetyl-4(5)-(1,2,3,4-tetrahydroxybutyl)imidazole (THI). To characterize and compare the effects of AC and THI and to study the influence of dietary pyridoxine, two studies in rats were conducted. Weanling rats fed a diet containing 2-3 ppm pyridoxine and exposed to 4% AC or 5.72 ppm THI in drinking water for 4 weeks showed reduced cell numbers in spleen and popliteal lymph nodes, as well as in the blood. Flow cytometric analyses demonstrated a comparable reduction in B and T lymphocytes. In blood, spleen, and popliteal lymph nodes, CD4+ lymphocytes were more reduced than CD8+ cells. The number of bone marrow cells was not affected. Although thymus weight and cell number were not affected either, a decreased cortex over medulla area ratio and an increase in medullary cell density largely due to an increase in CD4+ thymocytes was observed. Decreased numbers of ED2+ macrophages were observed in the thymic cortex and in the spleen red pulp. All effects observed were either less pronounced or absent in a study with rats fed a diet containing 11-12 ppm pyridoxine. The effects of AC and THI on the immune system were similar. Whereas AC exposure was associated with changes in vitamin B6 status, THI did not induce obvious effects on vitamin B6 parameters. It is proposed that the effects of AC and THI on the immune system are not caused by a disturbance of vitamin B6 metabolism, but may in fact result from a disturbance of a specific PLP-dependent process.

Functional restoration of ACD-blood by pyrodoxal 5'-phosphate

Successful application of pyridoxal 5'-phosphate (PLP) to restore the oxygen transport function of ACD-stored blood is described. PLP is readily incorporated into ACD-erythrocytes by both carrier-mediated transport (in which ATP may participate) and passive diffusion. Plasma proteins (up to 2.5%) and inorganic phosphate (up to 40 mM) do not affect the incorporation of PLP, though more than 25 mM inorganic phosphate is necessary for the maintenance of ATP levels. Increasing the PLP concentration and/or decreasing the packed cell volume in the medium, increases the incorporation of PLP. Incubation of erythrocytes with PLP at pH 7.0 is most suitable for incorporation of PLP and the maintenance of ATP levels. PLP incorporated into erythrocytes restores the oxygen transport function of the ACD-erythrocytes, though decreased haem--haem interaction is observed. A procedure for the clinical application of PLP-loaded erythrocytes is suggested.

Pyridoxine (pyridoxamine) phosphate oxidase activity in the red cell

A method has been developed for the measurement of red cell pyridoxine (pyridoxamine) phosphate oxidase activity. The more stable substrate, pyridoxamine phosphate, was incubated with a red cell haemolysate and the product pyridoxal phosphate was measured by Lactobacillus casei microbiological assay. A wide range of oxidase activities was found in control subjects (6-136 ng pyridoxal phosphate/g Hb x 10(-2)). There is a close correlation between the rate of conversion of pyridoxine to pyridoxal phosphate in whole blood and the oxidase activity. There was a marked increase in both after oral riboflavin. These results suggest that the oxidase plays a large part in the regulation of vitamin B-6 metabolism in red cells.

Vitamin B6 metabolism in anaemic and alcoholic man

Physiological and pathological factors affecting intracellular red cell vitamin B6 metabolism in normal, anaemic and alcoholic man were studied using a new assay for pyridoxine kinase (PnK) together with saturated and total aspartate aminotransferase (EGOT) activities as indirect indices of intracellular pyridoxal 5-phosphate (PLP) availability. In studies of anaemic states, subjects with iron deficiency anaemia demonstrated elevated levels of both PnK and saturated EGOT, while seven out of 17 subjects with inflammatory anaemia had subnormal PnK but variable saturated EGOT activities. Despite a high incidence of complicating inflammatory disease, alcoholic subjects with or without ring sideroblastic anaemia had elevated levels of both PnK and saturated EGOT. As judged from the saturated EGOT and the ratio unsaturated EGOT/saturated EGOT, intracellular PLP availability was always appropriate to the higher levels of PnK activity.

Pyridoxal kinase: decreased activity in red blood cells of Afro-Americans

The mean pyridoxal kinase activity in red blood cells of American blacks was approximately 50 percent lower than that of American whites. Lymphocytes, granulocytes, and cultured skin fibroblasts from black and white donors contained identical pyridoxal kinase activity. The pyridoxal kinase of blacks was indistinguishable from that of whites with respect to heat stability, chromatographic mobility on microgranular diethylaminoethyl cellulose, Michaelis-Menten constant for pyridoxine, and susceptibility to inhibition by 4-deoxypyridoxine. The difference of the activity of this enzyme in whites and in blacks is much greater than any previously observed biochemical difference between the races.